1. Field of the Invention
The present invention relates to a stable immunogen composition for oral administration.
2. Prior Art
An immunogen capable of immunizing human or animals is usually suspended in a buffered physiological saline for use. Such a suspension is referred to as vaccine. Examples of known vaccines are inactivated vaccines such as typhoid vaccine, pertussis vaccine, rabies vaccine and the like, attenuated live vaccines such as pathogenic micro-organism vaccine, live polio vaccine and the like, and toxoids such as diphtheria toxoid, tetanus toxoid and the like. An immunogen can be easily inactivated by physical factors such as temperature, light, shaking and the like since it consists mainly of proteins. Hence special care has been needed for preparation and storage of vaccines. It is known that saccharide or water-soluble gelatin (molecular weight: less than 20000) is added to a vaccine so as to improve in stability during storage.
Since vaccines are usually administered by injection, they tend to cause side effects such as redness, fever and amyotrophia in the administered region, shock and the like, beside being inconvenient administration.
In order to solve this problem, dosage forms of vaccine for oral administration have been proposed. A typical example of such dosage form is a powder or tablet preparation in which an immunogen is supported on a solid carrier such as lactose, saccharose and the like (Japanese Published Examined Patent Application No. 502262/1987). Further, it is known that cytochrome C, which is not an immunogen, is treated with gelatin of molecular weight of more than 50000 to form a composite material which is then formulated into various types of preparations for oral administration (Japanese Published Examined Patent Application No. 37971/1980).